Yemenis in Sana'a celebrate the departure of President Ali Abdullah Saleh to Saudi Arabia for medical treatment for wounds sustained in rocket attack. Photograph: Yahya Arhab/EPA

President Ali Abdullah Saleh's authoritarian grip on Yemen appeared to be slipping as he arrived in Saudi Arabia for medical treatment for wounds suffered in a rocket attack on his compound.

Saleh, whose Saudi medical evacuation plane was met by a senior Saudi official, walked off the aircraft but had visible injuries on his neck, head and face, a source told Reuters.

His journey to Saudi Arabia came amid speculation from Yemeni and western analysts that it was unlikely he would be able to return to Yemen if he was forced to seek medical assistance abroad.

Saleh delivered an audio address on television to reassure supporters, but his voice sounded laboured and the address was made accompanied by an old photograph of him on the screen.

A Saudi official, who asked not to be named, said: "He's here for medical treatment. We are the closest country and we have the capabilities." Asked whether Saleh was stepping down, the official said only: "He's coming for medical treatment."

There were celebrations in the Yemeni capital, Sana'a, following Saleh's departure, with thousands of people on the streets chanting and waving flags and banners.

Analysts fear that a sudden departure by Saleh, after 33 years in power, would leave a political vacuum and create even deeper chaos in Yemen, where the government has already lost control of some outlying provinces and where al-Qaida and other jihadists have appeared to exploit the political turmoil to move more freely.

There were reports on Sunday morning of heavy gunfire and explosions in Sana'a, just a day after a truce brokered by King Abdullah, who intervened in the conflict after almost four months of largely peaceful protests against Saleh spun out of control into an increasingly bloody civil conflict.

The gunfire was centred on the Hasaba district, a focal point of fighting in recent weeks between Saleh's forces and members of the powerful Hashid tribe led by Sadeq al-Ahmar.

Ahmar announced the Hashid's support for the protest movement in March, and his fighters adhered to the movement's non-violence policy. But last week, Saleh's forces moved against Ahmar's fortress-like residence in Sana'a, and the tribe's fighters rose up in fury.

Acting president Abd-Rabbu Mansour Hadi was due to meet members of the military and Saleh's sons, al-Arabiya television said on Sunday. It was the first indication that Saleh's powerful sons had not also left the country.

A leaderless Yemen would place enormous pressure on Saudi Arabia, which has long played the role of kingmaker for its much smaller, and infinitely poorer, neighbour.

The violence in the country grew out of pro-democracy protests that has turned into a power struggle between Saleh's ruling clique and his former allies in the Ahmar clan.

Sadeq al-Ahmar, the eldest of the Ahmar brothers, whose fighters have been battling Saleh's forces in the capital, confirmed that the Saudis had arranged a ceasefire, which he said he would respect. However, late on Saturday night, Ahmar accused Saleh's troops of not observing the ceasefire. He said the president's forces had not withdrawn from their positions in the city but were instead reinforcing those positions.

"We are respecting what we agreed upon under the guidance of the Saudi monarch to stop the bloodshed of innocents and bring safety for citizens based on our desire to bring security and quiet back to the capital, which is living through a terrible nightmare that Saleh's regime has brought upon it," Ahmar said.

The extent of the president's injuries has been a matter of intense speculation: when the rocket struck the mosque in his presidential compound, he was surrounded by senior officials and his bodyguards. Eleven guards died and five officials standing near the president were seriously wounded. They have already gone to Saudi Arabia for treatment.

Yemen TV denies reports on al-Jazeera that President Ali Abdullah Saleh's family have fled the country with him to Saudi Arabia, while opposition protesters celebrate Saleh's departure in al-Taghyeer Square